The present invention relates to a vehicle internal combustion engine exhaust system.
The performance of an internal combustion engine in terms of output and the manner in which this is supplied (i.e. the characteristic curve of the engine) is known to depend, not only on the engine itself, but also on the exhaust system, the characteristics of which in turn depend on the type and degree of noise attenuation required.
At the design stage, therefore, a trade-off is invariably involved between the characteristics of the engine and the exhaust system, and which generally results in impaired performance of the engine, particularly at high speed, due to the conflicting exhaust system design features required for achieving given performance characteristics at both high and low engine speeds. On catalyzed engines of high-performance (so-called Grand Touring) vehicles, operation of the catalyst has also been found to be impaired at high engine speed, due to the fuel supply system supplying a "richer" air/fuel mixture, i.e. having a lower dilution coefficient.